1. Field of the Invention
The present invention relates to an image reading device that converts light passed through an original image into electrical signals using a photoelectric conversion element, such as a CCD (Charged Coupled Device) camera, and, more particularly, to such an image reading device capable of masking a specified range of the original image.
2. Description of the Related Art
In the aforementioned field, it is known to use devices such as shading sheets to block out unwanted portions of image light being projected from a translucent original, such as a negative or a transparency. Borders and excess image areas are typically blocked out in this manner. Conventionally, such as shown in FIG. 10, several shading sheets are cut so as to block out these unwanted areas when placed on and around the original. The user would then stack the shading sheets on the original before transmitting light therethrough.
Most image reading devices use an original cassette glass for holding the image. An original holding glass is typically placed over top of the original to secure it in place. Light is transmitted through the original and recorded as electrical signals by a photoelectric conversion element, such as a CCD output. Currently, equipment designed to digitize originals must rely on shading sheets to eliminate excess areas. The shading sheets are held between the cassette glass and the holding glass with the image. As the light cannot pass through the shielding, the camera only sees those regions of the image which the user wishes to be recorded.
Each image to be processed in the aforementioned manner requires a different set of shields to achieve the desired results. Even if only the clear borders of each image are masked, there is still a need for multiple shading sheets, one for each size of original to be processed. There is a practical limit to the different types of sheets that can be prepared, thus limiting the user to a defined number of formats and shading schemes. It is also difficult to maintain the full set of shielding sheets due to the inevitable damage and loss of such sheets. As such, there exists a need for an apparatus and a method for masking an area of an original without using light shielding sheets.